Frank Sinatra is universally recognized as one of the greatest voices of the 20th century. He was also an equally talented actor. But his fame as a singer overshadowed his screen legacy. Tom Santopietro devoted his new book, Sinatra in Hollywood, to shining a spotlight on Sinatra's film career.

To write about Sinatra's screen legacy, Santopietro had to watch a lot of movies.

"Sinatra appeared in around 70 films, in cameo or starring roles," he says. "So there was a great deal of film to look at. And I read everything I could find about Sinatra. There are dozens of books and thousands of newspaper articles.

"And then I sat down and watched every one of his films at least once, in some cases, several times. And you know, Frank was the first to say that some of his films were not classic, but the great ones were absolutely terrific."

Santopietro says, when given the right material, Sinatra proved himself a gifted artist.

"I think what made him so great on screen was that he was able to access these very deep emotions," he says. "And I think that's because of his training as a singer. He was used to telling a story in song. On screen, Sinatra was a tough guy, but he was not afraid to show his vulnerability, and that was a new kind of figure on screen. That's what made him so interesting to watch and actually why audiences today can still identify with him."

Film achievements top Sinatra's list of career highlights

What surprised the author is how seriously Sinatra took his career in Hollywood.

"I think people don't realize that he really wanted to be a movie star," he says. "He was determined to make it, which he did. I came across an interesting interview he did with Johnny Carson on the Tonight Show in the 1970s, so Sinatra had been a star for decades.

"Johnny Carson said to him, 'You have an unparalleled career. What's the highlight?' Sinatra instantly said, 'Winning the Oscar for From Here to Eternity and making The Man with the Golden Arm.' What was surprising to me was he didn't say the music. He didn't say the Grammy Awards. He instantly talked about the movies."

Sinatra was at his peak as a singer and an actor in the 1950s, Santopietro says.

"In 1955 alone, he released five movies, which he starred in," he says. "Nobody would ever do that today. They were, all but one, big hits and terrific performances. So I say that Sinatra at that point was in many ways like America. Both were really on a roll, and the toughest times lay ahead, but at that point, as Frank Sinatra was singing, 'I've Got the World on a String,' and he really did."

Rat Pack movies put Las Vegas on the map

Among Sinatra's most popular movies of those years were the ones he made with a group of actor friends who were known as the Rat Pack.

"The Rat Pack still fascinates people today, 50 years later," he says. "It was Frank Sinatra, Dean Martin, Sammy Davis Jr., Peter Lawford and Joey Bishop. It was really right around 1960. They were in [Las] Vegas. Sinatra slept only four hours a night because he'd make a movie at the same time he'd be singing in the nightclubs. He'd be out carousing with his pals.

"That really put Vegas on the map. Vegas exploded as an adult playground, and I think it made Frank loom larger than life. There he was, also palling around with President-elect [John F.] Kennedy.

"The best of the Rat Pack movies is Oceans Eleven, which of course has been remade by George Clooney. That's really a fun movie."

Bing Crosby, mother among artist's influences

In his book, Santopietro examines the influences that helped shape Sinatra's career, including the crooner Bing Crosby.

"When Sinatra was unknown, he went to see Bing Crosby sing, and afterwards he turned to his date, who eventually became his first wife, Nancy [Barbato] and said, 'That's going to be me up there someday,'" he says. "Then when he saw Bing Crosby also became a movie star, Sinatra wanted that same sort of career, where he could succeed in both."

Sinatra's mother, Dolly, was also a very influential figure in his personal life and career.

"Nobody ever told Frank Sinatra what to say or what to do except his mother," he says. "Dolly was outgoing. She was influential in Democratic politics. She was a mover and a shaker, you know, at a time when very few women were. She was in many ways a pioneer.

"She loved Frank, but they continually squabbled. They were both so strong-willed. He always wanted to prove to his mother that he could be somebody, that he could be a star. That was the engine inside of him."

In Sinatra in Hollywood, Santopietro also examines Sinatra's relationships with his leading ladies.

"He was a great actor to play opposite, if you were quick," he says. "If you were not quick, he would get very impatient. But he generally had really good relationships with his co-stars. Of course, in terms of relationship with the famous women, the most famous, of course, is his kind of legendary romance with Ava Gardner. They both couldn't live without each other, and they couldn't live with each other. That's why that romance still fascinates people today."

Sinatra 'the actor' surpasses Sinatra 'the singer'

In spite of his on-screen success, Santopietro says Sinatra had a hard time finding roles as he got older.

"The roles are not there for older people in Hollywood," he says. "It is so youth-oriented, even more today. Sinatra, in fact, hired his daughter, Tina, to scout material for him. He really wanted to keep making movies. But they were not writing movies for 60-, 65-, 70-year-old men. So it was very difficult for him to find the right material, and I think that was a great frustration for him.

"At the same time, I say in the book, at the end of his life, I actually think Sinatra the actor had surpassed Sinatra the singer because his voice had deteriorated with age, but as an actor, he just kept growing and growing. It was really remarkable to see his final performances."

Santopietro says he hopes he can inspire the younger generation to explore Sinatra's cinematic legacy. He also hopes his book will make people think of Sinatra in a new light, not as just a singer or a celebrity but as a significant part of Hollywood history.